Piezo-phototronic effect devices

ABSTRACT

A semiconducting device includes a piezoelectric structure that has a first end and an opposite second end. A first conductor is in electrical communication with the first end and a second conductor is in electrical communication with the second end so as to form an interface therebetween. A force applying structure is configured to maintain an amount of strain in the piezoelectric member sufficient to generate a desired electrical characteristic in the semiconducting device.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/473,345, filed Apr. 8, 2011, the entirety ofwhich is hereby incorporated herein by reference.

STATEMENT OF GOVERNMENT INTEREST

This invention was made with government support under contract No.DE-FG02-07ER46394, awarded by the Department of Energy. The governmenthas certain rights in the invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to semiconducting devices and, morespecifically, to a piezoelectric semiconductor device.

2. Description of the Related Art

Semiconductor devices are used in many different applications, includingdiodes, transistors, light emitting devices and sensing devices. Whilesuch semiconducting devices can be considerably more efficient thantheir macro-scale electrical counterparts, they still use a considerableamount of energy. Such energy usage can result in severaldisadvantageous phenomena, such as increased heat output and shortenedbattery life.

Therefore, there is a need for semiconducting structures with greaterefficiency.

SUMMARY OF THE INVENTION

The disadvantages of the prior art are overcome by the present inventionwhich, in one aspect, is a semiconducting device that includes apiezoelectric structure that has a first end and an opposite second end.A first conductor is in electrical communication with the first end anda second conductor is in electrical communication with the second end soas to form an interface therebetween. A force applying structure isconfigured to maintain an amount of strain in the piezoelectric membersufficient to generate a desired electrical characteristic in thesemiconducting device.

In another aspect, the invention is a method of making a semiconductingdevice, in which a piezoelectric member, having a first end and anopposite second end, is placed on a flexible substrate. A firstconductor is affixed to the first end. A second conductor is affixed tothe second end so as to form an interface therebetween. The secondconductor includes a material that forms with the piezoelectric memberat the interface a selected one of a p-n junction or a Schottky contact.A predetermined amount of strain is applied to the piezoelectric memberso as to generate a desired electrical characteristic in thesemiconducting device.

These and other aspects of the invention will become apparent from thefollowing description of the preferred embodiments taken in conjunctionwith the following drawings. As would be obvious to one skilled in theart, many variations and modifications of the invention may be effectedwithout departing from the spirit and scope of the novel concepts of thedisclosure.

BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWINGS

FIG. 1 is a schematic diagram of a light emitting semiconducting device.

FIG. 2A is a schematic energy band diagram demonstrating bandrelationships in piezoelectric semiconducting devices with differentamounts of strain applied thereto.

FIG. 2B is a schematic diagram demonstrating stress being applied to apiezoelectric structure and corresponding piezopotentials resultingtherefrom.

FIG. 3 is a schematic diagram of a light detecting device.

FIG. 4 is a graph relating absolute current to excitation intensitydetected in the device shown in FIG. 3.

FIGS. 5A-5B are schematic diagrams of piezoelectric semiconductingswitching devices.

DETAILED DESCRIPTION OF THE INVENTION

A preferred embodiment of the invention is now described in detail.Referring to the drawings, like numbers indicate like parts throughoutthe views. Unless otherwise specifically indicated in the disclosurethat follows, the drawings are not necessarily drawn to scale. As usedin the description herein and throughout the claims, the following termstake the meanings explicitly associated herein, unless the contextclearly dictates otherwise: the meaning of “a,” “an,” and “the” includesplural reference, the meaning of “in” includes “in” and “on.”

U.S. patent application Ser. No. 12/945,077 filed Nov. 12, 2010 by Wanget al. discloses methods of making piezo-phototronic devices and isincorporated herein by reference.

As shown in FIG. 1, one embodiment of a piezoelectric semiconductorincludes a light emitting device 100. This embodiment includes apiezoelectric structure 110 that can include, for example, ZnO, GaN, ora wurtzite structured material. In one embodiment, the piezoelectricstructure 110 includes a ZnO nanowire. An ITO film 122 is deposited onan Al₂O₃ substrate 120 and a conductor 112 is placed in electricalcommunication with both the ITO film 122 and the piezoelectric structure110. Another Al₂O₃ substrate 124 has an Mg-doped GaN film 126 depositedthereon. The piezoelectric structure 110 is affixed to the Mg-doped GaNfilm 126 by an attaching substance 116 and a conductor 114 is placed inelectrical communication with the Mg-doped GaN film 126. A gap 128 isdefined between the two Al₂O₃ substrates 122 and 124 and it is bridgedby the piezoelectric structure 110. The two Al₂O₃ substrates 122 and 124are affixed to a polyimide film 134 (such as Kapton). A clear rigidplate 132 (such as a sapphire plate) has a resilient pad 130 (such as apiece of polystyrene) affixed thereto. The transparent resilient layer130 is placed against the piezoelectric structure 110. A force isapplied to the polyimide film 134 by means of a metal rod 136, whichcauses differential bending of the piezoelectric structure 110, therebymaintaining a strain therein. When a voltage source 138 applies apotential between the electrical contacts 112 and 114, the device emitslight.

In one experimental embodiment, the piezo-phototronic effect has beeneffectively utilized to enhance the external efficiency of an LED 100fabricated using a single ZnO micro-/nano-wire 110 on a GaN substrate126. The emission light intensity and injection current at a fixedapplied voltage has been enhanced by a factor of 17 and 4 after applyinga 0.093% compressive strain, respectively, and the correspondingconversion efficiency was improved by a factor of 4.25. This issuggested arising from an effective increase in the local “biasedvoltage” as a result of the band modification caused by piezopotentialand the trapping of free carriers at the interface region in a channelcreated by the piezopotential near the interface. Furthermore, thepiezoresistance and piezooptic (photoelastic) effects have been utilizedto tune the light emitting intensity, spectra and polarizationsimultaneously. The piezo-phototronic effect can be effectively used forenhancing the efficiency of energy conversion in today's safe, green andrenewable energy technologies.

A single ZnO micro-/nanowire LED 100 was fabricated by manipulating aZnO wire 110 on a trenched substrate. A Mg doped p-type GaN film 126 wasepitaxially grown on a sapphire substrate 124 by metal organic chemicalvapor deposition (MOCVD) and was used to form a p-n junction with n-typeZnO wire 110. An ITO coated 122 sapphire substrate 120 was used as thecathode that was placed side-by-side with the GaN substrate 126 with awell-controlled gap 128. The ZnO wire 110 was placed across the gap 128with a close contact with the GaN film 126. A transparent polystyrene(PS) tape 130 was used to cover the ZnO nanowire 110. A normal force wasapplied on the PS film 130 by an alumina rod 136 connected to a piezonano-positioning stage (not shown). In this case, a compressive stresswas applied uniformly normal to the interface between the side surfaceof the ZnO wire 110 and the GaN substrate surface 126. Such acompressive force along the a-axis of the ZnO wire 110 resulted in atensile strain along the c-axis, the growth direction of the wire 110.In this embodiment, there was no transverse bending or twist on the wire110 to ensure the stability of the p-n junction interface between theZnO wire 110 and GaN substrate 126.

The external efficiency of an as-fabricated single wire LED was measuredconservatively to be about 1.84% before applying a strain, which is ashigh as that for a single p-n junction based UV LED. To test the straineffect on a single ZnO wire LED, the experiment systematicallyinvestigated its output light intensity, electroluminescence spectra andpolarization as the strain being applied. At a fixed applied bias abovethe turn-on voltage (3 V), the current and light emission intensityincreased obviously with increase of the compressive strain. Thesignificantly enhanced light intensity was also directly observed inoptical images recorded by a CCD. The injection current and output lightintensity were largely enhanced by a factor of 4 and 17, respectively,after applying a 0.093% a-axis compressive strain, indicating that theconversion efficiency was improved by a factor of 4.25 in reference tothat without applying strain. This means that the external trueefficiency of the LED can reach about 7.82% after applying a strain.

To confirm the validity of the observed data, the stability of thecontact between ZnO wire and GaN was carefully examined by repeating theapplied strain. Once the strain was retracted, the light emissionintensity dropped back to the value observed at strain free case. Alinear relationship observed in the enhancement factor with strainproved that a possible change in contact area between n- and p-side ofthe device was not responsible to the observed increase in efficiency.

As shown in FIGS. 2A and 2B, when the n-ZnO wire/p-GaN substrate LED isunder axial straining, two typical effects influence the output lightintensity and spectra. One is the piezoresistance effect, which iscaused by the change in bandgap and possibly density of states in theconduction band. This effect acts as adding a serial resistance to theLED. The second effect is the piezo-phototronic effect, which is aboutthe tuning of the optoelectronic process at the interface using thepiezopotential created along the ZnO wire. ZnO has a non-centralsymmetric crystal structure, in which the cations and anions aretetrahedrally coordinated. A straining on the basic unit results in apolarization of the cations and anions, which is the cause of thepiezopotential inside the crystal. As for the ZnO (n-type)—GaN (p-type)LED, a schematic diagram of its band structure is presented in FIG. 2A.Since the size of the GaN substrate is much larger than that of the ZnOmicrowire, the strain in GaN is much smaller than that in ZnO, thus thefocus is on the piezoelectric effect from ZnO. Under an assumption ofno-doping or low-doping in ZnO for simplicity, numerically calculatedpiezopotential distribution in the ZnO microwire, as shown in FIG. 2B,shows that a negative potential drop is created along its length whenthe ZnO microwire is under a-axis compressive strain. The finite dopingin the wire may partially screen the piezoelectric charges, but itcannot totally eliminate the piezoelectric potential if the doping levelis low, thus a dip in the band is possible. The low-doping in ZnO wirehere is consistent with our experiment results because the ZnO wire isfabricated by a high-temperature thermal evaporation process using pureZnO powders as the source. If the c-axis of the ZnO wire is pointingfrom the ITO side to the GaN side, as shown in FIG. 2B, the effect ofthe local negative piezopotential at the ITO side is equivalent toapplying an extra forward biased voltage on the device. Thus, thedepletion width and internal field are reduced under this additionalcomponent of forward biased voltage. Subsequently, the injection currentand emitting light intensity under the same externally applied forwardvoltage increase when the device is strained. Alternatively, if thec-axis of the ZnO wire is reversed and pointing away from the GaN side,the GaN side has a lower piezopotential, which is equivalent to applyingan extra reversely biased voltage on the device. The depletion width andinternal field are thus increased, resulting in a reduction of theinjection current and emitting light intensity with the increase of theapplied strain.

The light output of LED is proportional to the external efficiency andinjection current. Meanwhile, the injection current across the p-njunction increases exponentially with the increase of the forward biasvoltage (for V>>kT/q) according to the Shockley equation. Therefore, thechange in light emission intensity under strain can be described by):

${\ln\left( \frac{\Phi_{out}(ɛ)}{\Phi_{out}(0)} \right)} = {{{\ln\left( \frac{I(ɛ)}{I(0)} \right)} + \left( \frac{\eta_{ex}(ɛ)}{\eta_{ex}(0)} \right)} = {\frac{\Delta\;\psi}{kT} + {f(ɛ)}}}$where η_(ex)(ε) and η_(ex)(0) represent the output external efficiencyof LED with and without applying a strain, respectively, k is theBoltzmann constant, T is temperature, and f(ε) represents the effect ofstrain on external efficiency.

The enhancement factor for light emission was larger than that for theinjection current, which means that the quantum efficiency was enhancedwith the increase of strain according to the above equation. By solvingPoisson equation with coupling piezoelectric effect, the enhancement ofexternal efficiency may be caused by the localized positivepiezopotential near GaN/ZnO interface, which produces carrier trappingchannels (as shown in FIG. 2A). Electrons and holes can be temporarilytrapped and accumulated in the channels in the conduction and valanceband, respectively. Since abundant electrons are available in ZnO, forinstance, the efficiency of the LED is largely dominated by the localconcentration of holes because of the high activation energy of the mostcommonly used acceptor dopants (Mg) in GaN (˜200 meV). The trapped holesmay increase the hole injection from p-GaN into n-ZnO, which increasesthe recombination efficiency of electrons and holes near the junction,resulting in a large increase in emission intensity. It is pointed outthat, though the absolute values of the band offset varies in differentreports, and is dependent on the fabrication process of theheterojunction, the band offset values do not affect the tendency of theband modification and the profile of the carrier trapping channel bypiezopotential.

The peak positions of the four emission bands did not exhibit anyappreciable shift under straining, but they did have obvious blue shiftas the applied bias voltage was increased. The bandgap of ZnO decreasesunder compressive a-axis strain, while the bandgap of GaN also decreasesunder compressive c-axis strain. In this case, the peak position shouldhave a red shift under compressive strain. On the other hand, theemission centers of the n-ZnO/p-GaN LED have blue shift with theincrease of injection current due to the band renormalization, bandfilling at high current and/or the increased kinetic energies ofelectrons and holes. When these two complementary effects co-exist, onemay balance the other, resulting in negligible shift in emission peaks.The change in refraction index of ZnO is also possible under strain,which is the photoelastic effect.

The performance of an LED is dictated by the structure of the p-njunction and the characteristics of the semiconductor materials. Once anLED is made, its efficiency is determined largely by the local chargecarrier densities and the time at which the charges can remain at thevicinity of the junction. The latter is traditionally controlled bygrowing a quantum well or using a built-in electronic polarization for“trapping” electrons and holes in the conduction and valance bands,respectively. Instead of using this pre-fabricated structure, thepiezopotential is created in ZnO by strain to control the chargetransport process at the ZnO—GaN interface, demonstrating the first LEDwhose performance is controlled by piezoelectric effect. The emissionintensity and injection current at a fixed applied voltage have beenenhanced by a factor of 17 and 4 after applying a 0.093% compressivestrain, respectively, and the corresponding conversion efficiency hasbeen improved by a factor of 4.25 in reference to that without applyingstrain! And an external efficiency of 7.82% has been achieved. Thissignificantly improved performance is not only attributed to theincrease of injection current by the modification of the band profile,but also to the effect of the creation of a trapping channel for holesnear the heterojunction interface, which greatly enhances the externalefficiency. An increase in UV-to-visible ratio and stabilization of thepeak position show that the spectrum quality is improved by externalstraining. In addition, the polarization of the output light has beenmodulated by the piezooptic effect. This discovery is important not onlyfor exploring the piezo-phototronic effect through a three-way couplingamong mechanical, electronic and optical properties, but also canlargely improve the efficiency and performance of LEDs and the design ofa large range of optoelectronic devices based on ZnO and GaN with theuse of their piezoelectric property.

In another embodiment, as shown in FIG. 3, the device may be configuredas a photo detector 300. An experimental version of this embodimentincludes a metal-semiconductor-metal structure (MSM). The contacts 312and 314 at the two ends of the semiconductor wire 310 are twoback-to-back Schottky contacts. The device was fabricated by bonding aZnO micro/nanowire 310 laterally on a polystyrene (PS) substrate 330,which has a thickness much larger than the diameter of the ZnOmicro/nanowire 310. The mechanical behavior of the device was dominatedby the substrate by considering the relative size of the wire 310 andthe substrate 330. Strain was induced in the nanowire 310 by twostrain-inducing structures 340 that were coupled to opposite ends of thePS substrate 330. A bias voltage from a voltage source 338 was appliedto the contacts 312 and 314. The strain in the wire 310 was mainly axialcompressive or tensile strain depending on the bending direction of thePS substrate 330, and it was quantified by the maximum deflection of thefree end of the substrate. Monochromatic UV, blue and green light 334from a light source 342 illuminated the ZnO wire 310 to test theperformance of the device. The photocurrent flowing through the nanowire310 was a function of the intensity of the light 344 and the straininduced in the nanowire 310.

The ZnO micro/nanowires used in one experimental embodiment weresynthesized by a high-temperature thermal evaporation process. A singleZnO wire 310 was bonded on a PS substrate 330 (typical length of about 7cm, a width of about 15 mm and thickness of 0.5 mm) with silver paste. Avery thin layer of polydimethylsiloxane (PDMS) (not shown) was used topackage the device, which kept the device mechanically robust underrepeated manipulation and prevented the semiconductor wire fromcontamination or corrosion. A 3D stage 340 with movement resolution of 1μm was used to bend the free end of the device to produce a compressiveand tensile strain. Another 3D stage 340 was used to fix the sampleunder microscope and to keep the device in focus during the substratebending process.

A Nikon Eclipse Ti inverted microscope system was used to monitor thesample and excite the photodetector. A Nikon Intensilight C-HGFIE lampwith a remote controller was used as the excitation source 342.Monochromatic UV (centered at 372 nm), blue (centered at 486 nm) orgreen light (centered at 548 nm) was illuminated on the ZnO wire to testthe performance of the device, which was focused by a 10× microscopeobjective with a 17.5 mm work distance. Monochromatic light was obtainedby a filter block between the source and microscope objective. Therewere three sets of filter blocks which used to obtain monochromatic UV,blue and green light. The optical power density impinging on thenanowire photodetector was varied by means of neutral density filters.The illumination density was determined by a thermopile power meter(Newport 818P-001-12). I-V measurement was obtained by applying anexternal bias to the wire and recorded using a Keithley 487picoammeter/voltage source in conjunction with a GPIB controller(National Instruments GPIB-USB-HS, NI 488.2). In order to compare andanalyze the results, time dependent photocurrent, light intensitydependent photocurrent and photocurrent used for analyzing responsivityand strain effects were measured at a fixed applied bias of −5 V fromthe voltage source 338.

As shown in FIG. 4, the photocurrent increased linearly with the opticalpower and showed no saturation at high power levels, offering a largedynamic range from sub-μW/cm² to mW/cm². The total responsivity of thephotodetector,

, is defined as

$\begin{matrix}{= {\frac{I_{ph}}{P_{ill}} = {\frac{\eta_{ext}q}{hv} \cdot \Gamma_{G}}}} & (1) \\{P_{ill} = {I_{ill} \times d \times l}} & (2)\end{matrix}$where

is the responsivity, I_(ph) photocurrent, P_(ill) the illumination poweron the photodetector, η_(ext) the external quantum efficiency, q theelectronic charge, h Planck's constant, v the frequency of the light,Γ_(G) the internal gain, I_(ill) the excitation power, d the diameter ofthe ZnO wire, l is the spacing between two electrodes. Remarkably, thecalculated responsivity of the device is super high, approximately4.5×10⁴ A W⁻¹ at an intensity of 0.75 μW/cm² of UV light illumination.The internal gain can be estimated to be 1.5×10⁵ by assuming η_(ext)=1for simplicity. The high internal gain and high responsivity isattributed to the oxygen-related hole trapping states and the shrinkingof the Schottky barrier upon illumination.

This embodiment behaves as a single ZnO wire sandwiched between twoback-to-back Schottky diodes. When a relatively large negative voltagewas applied, the voltage drop occurred mainly at the reversely biasedSchottky barrier φ_(d) at the drain side, which is denoted as V_(d)≈V.Under reverse bias and in the dark condition, thermionic emission withbarrier lowering is usually the dominant current transport mechanism ata Schottky barrier, which can be described by thethermionic-emission-diffusion theory (for V>>3 kT/q˜77 mV) as:

$\begin{matrix}{I_{TED}^{dark} = {{SA}^{**}T^{2}{\exp\left( {- \frac{q\;\phi_{d}^{dark}}{kT}} \right)} \times {\exp\left\lbrack {}^{4}{\sqrt{\frac{q^{7}{N_{D}\left( {V + V_{bi} - \frac{kT}{q}} \right)}}{8\;\pi^{2}s_{s}^{s}}}/{kT}} \right\rbrack}}} & (3) \\{\mspace{79mu}{V_{bi} = {\phi_{d}^{dark} - \left( {E_{C} - E_{f}} \right)}}} & (4)\end{matrix}$in which S the area of the Schottky contact, A** the effectiveRichardson constant, T the temperature, q the unit electronic charge, kthe Boltzmann constant, N_(D) the donor impurity density, V the appliedvoltage, V_(bi) the built-in potential, and ε_(s) the permittivity ofZnO.

The effect of photo illumination on semiconductor thermionic emission isto lower the energy barrier by the difference between the quasi-Fermilevel with photoexcitation and the Fermi level without photoexcitationand to reduce the width of depletion layer by photon generated holestrapping in the depletion layer. The current transport mechanism withillumination can be describes as:

$\begin{matrix}\begin{matrix}{I_{TED}^{ill} = {{SA}^{**}T^{2}{\exp\left( {- \frac{q\left( {\phi_{d}^{dark} - \left( {E_{FN} - E_{f}} \right)} \right)}{kT}} \right)} \times}} \\{\exp\left\lbrack {}^{4}{\sqrt{\frac{q^{7}{N_{D}\left( {V + V_{bi} - \frac{kT}{q}} \right)}}{8\pi^{2}s_{s}^{s}}}/{kT}} \right\rbrack} \\{= {{SA}^{**}T^{2}{\exp\left( {- \frac{q\;\phi_{d}^{iii}}{kT}} \right)} \times {\exp\left\lbrack {}^{4}{\sqrt{\frac{q^{7}{N_{D}\left( {V + V_{bi} - \frac{kT}{q}} \right)}}{8\pi^{2}s_{s}^{s}}}/{kT}} \right\rbrack}}}\end{matrix} & (5)\end{matrix}$where E_(FN) is quasi Fermi level with illumination.

By assuming S, A**, T, N_(D) are independent of strain at smalldeformation, the change of Schottky barrier height (SBH) with strainupon illumination can be determined by:

$\begin{matrix}{\mspace{79mu}{{\ln\left( \frac{l\left( t_{xx} \right)}{l(0)} \right)} = {{- {\Delta\phi}_{d}^{ill}}/{kT}}}} & (6)\end{matrix}$where I(ε_(xx)) and I(0) are the current measured through the ZnO wireat a fixed bias with and without strain applied, respectively.

The contributions from band structure effect to SBH in source and draincontacts are denoted as Δφ_(d-bs) and Δφ_(s-bs), respectively. Assumingthe axial strain is uniform in the ZnO wire along its entire length,Δφ_(d-bs)=Δφ_(s-bs) if the two contacts are identical. This is thepiezoresistance effect, which is symmetric and has equal effectsregardless the polarity of the voltage. The asymmetric change of I-Vcurve at negative and positive bias in our case is dominated bypiezoelectric effect rather than piezoresistance effect. The effect ofpiezopotential to the SBH can be qualitatively described as follows. Fora constant strain of ε_(xx) along the length of the wire, an axialpolarization P_(x)=ε_(xx)e₃₃ occurs, where e₃₃ is the piezoelectrictensor. A potential drop of approximately V_(p) ⁺−V_(p) ⁻=ε_(xx)Le₃₃ isalong the length of the wire, where L is the length of the wire.Therefore, the modulations to the SBH at the source and drain sides areof the same magnitude but opposite sign (V_(p) ⁺=−V_(p) ⁻), which aredenoted by Δφ_(d-pz) and Δφ_(s-pz) (Δφ_(d-pz)=−Δφ_(s-pz)).

This embodiment includes a piezopotential tuned low dark-currentultrasensitive ZnO wire photodetector. The device remains low darkcurrent characteristics while increasing the responsivity dramaticallyfor pW level light detection by piezopotential. The derived change ofbarrier height with strain depends on excitation light intensity, theSBH changes faster at low light intensity than that at high lightintensity. The physical mechanism is explained by considering bothpiezopotential effect and photon generated free charges screeningeffect. Three-way coupling of semiconducting, photonic and piezoelectricproperties of semiconductor nanowires will allow tuning and controllingof electro-optical process by strain induced piezopotential, which isthe piezo-phototronic effect, and it will also lead to furtherintegration between piezoelectric devices with microelectronic andoptomechanical systems.

Another embodiment, as shown in FIGS. 5A-5B, includes a switchingstructure 500 that behaves like a transistor. The piezotronic transistorstructure 500 includes a metal 512—nanowire 510—metal 514 structure thatis biased by a voltage source 538. The metal portions 512 and 514 caninclude metals such as Au or Ag. In one embodiment, the nanowire 510includes ZnO. The principle of the piezotronic transistor is to controlthe carrier transport at the M-S interface through a tuning at the localcontact by creating a piezopotential at the interface region in thesemiconductor by applying a strain. This structure is different from atypical MOS design, in that the externally applied gate voltage isreplaced by an inner crystal potential generated by piezoelectriceffect, thus, the “gate” electrode can be eliminated. This means thatthe piezotronic transistor needs only two leads: drain and source.Secondly, the control over channel width is replaced by a control at theinterface. Since the current transported across an M-S interface is theexponential of the local barrier height at the reversely biased case,the ON and OFF ratio can be rather high due to the non-linear effect.Finally, a voltage controlled device is replaced by an externalstrain/stress controlled device, which is likely to have complimentaryapplications to CMOS devices.

The device 500 under tensile strain is shown in FIG. 5A and the device500 under compressive strain is shown in FIG. 5B. When a ZnO nanowiredevice is under strain, there are two typical effects that may affectthe carrier transport process. One is the piezoresistance effect becauseof the change in band gap, charge carrier density and possibly densityof states in the conduction band of the semiconductor crystal understrain. This effect is a symmetric effect on the two end contact and hasno polarity, which will not produce the function of a transistor.Piezoresistance is a common feature of any semiconductors such as Si andGaAs and is not limited to the wurtzite family. The other is thepiezoelectric effect because of the polarization of ions in a crystalthat has non-central symmetry, which has an asymmetric or non-symmetriceffect on the local contacts at the source and drain owing to thepolarity of the piezopotential. In general, the negative piezopotentialside raises the barrier height at the local contact of metal n-typesemiconductor, possibly changing a Ohmic contact to Schottky contact, aSchottky contact to “insulator” contact; while the positivepiezopotential side lowers the local barrier height, changing a Schottkycontact to an Ohmic contact. But the degree of changes in the barrierheights depends on the doping type and doping density in the nanowire.The piezoelectric charges are located at the ends of the wire, thus theydirectly affect the local contacts. The piezotronic effect is likelylimited to the wurtzite family such as ZnO, GaN, CdS and InN. Thepolarity of the piezopotential can be switched by changing tensilestrain to compressive strain. Thus, the device can be changed from acontrol at source to a control at drain simply by reversing the sign ofstrain applied to the device.

The above described embodiments, while including the preferredembodiment and the best mode of the invention known to the inventor atthe time of filing, are given as illustrative examples only. It will bereadily appreciated that many deviations may be made from the specificembodiments disclosed in this specification without departing from thespirit and scope of the invention. Accordingly, the scope of theinvention is to be determined by the claims below rather than beinglimited to the specifically described embodiments above.

What is claimed is:
 1. A semiconducting device, comprising: (a) apiezoelectric structure, having a first end and an opposite second end;(b) a first conductor in electrical communication with the first end;(c) a second conductor in electrical communication with the second endso as to form an interface therebetween; (d) a force applying structureconfigured to maintain an amount of strain in the piezoelectric member;and (e) a voltage source configured to apply a potential between thefirst conductor and the second conductor, wherein the piezoelectricstructure emits light as a function of the amount of strain applied bythe force applying structure and the potential applied between the firstconductor and the second conductor.
 2. The semiconducting device ofclaim 1, wherein the second conductor includes a material that formswith the piezoelectric member at the interface a selected one of a p-njunction or a Schottky contact.
 3. The semiconducting device of claim 2,wherein a desired electrical characteristic exhibited at the interfacecomprises a predetermined band relationship at the interface.
 4. Thesemiconducting device of claim 1, further comprising a non-conductiveflexible substrate upon which the piezoelectric structure is disposed.5. The semiconducting device of claim 1, wherein the piezoelectricstructure comprises a selected one of a nanowire or a one-dimensionalshape structure.
 6. The semiconducting device of claim 1, wherein thepiezoelectric structure comprises a selected one of ZnO, GaN, or awurtzite structured material.
 7. The semiconducting device of claim 1,wherein the first conductor comprises a material selected to form anOhmic contact with the piezoelectric structure.
 8. A semiconductingdevice configured as a light emitting device, comprising: (a) apiezoelectric structure including a wurtzite nanowire, having a firstend and an opposite second end; (b) a first conductor in electricalcommunication with the first end; (c) a second conductor in electricalcommunication with the second end so as to form an interfacetherebetween; and (d) a force applying structure configured to maintainan amount of strain in the piezoelectric member sufficient to generate adesired electrical characteristic in the semiconducting device; (e) aMg-doped GaN film deposited on a first Al₂O₃ substrate, the firstconductor in electrical communication therewith; (f) an ITO filmdeposited on a second Al₂O₃ substrate, the second conductor inelectrical communication therewith, the second Al₂O₃ substrate spacedapart from the first Al₂O₃ substrate so as to define a gap having apredetermined width therebetween, the wurtzite nanowire being placedacross the gap; and (g) a voltage source electrically coupled to boththe Mg-doped GaN film and the ITO film so as to be configured togenerate a potential difference therebetween; (h) a polyimide filmdisposed on the force applying structure and on which is disposed boththe first Al₂O₃ substrate and the second Al₂O₃ substrate; and (i) atransparent resilient layer disposed against wurtzite nanowire, theMg-doped GaN film and the ITO film.
 9. The semiconducting device ofclaim 8, wherein the force applying structure comprises an alumina rodconfigured to apply a force in a direction that is normal to an axis ofthe wurtzite nanowire.
 10. A photodetector for detecting light from alight source, comprising: (a) a piezoelectric structure, having a firstend and an opposite second end; (b) a first conductor in electricalcommunication with the first end and including a first metal that formsa Schottky contact therewith; (c) a second conductor in electricalcommunication with the second end and including a second metal thatforms a Schottky contact therewith; (d) a strain-inducing structureconfigured to maintain an amount of strain in the piezoelectric member;and (e) a voltage source configured to apply a bias potential betweenthe first conductor and the second conductor, the bias potential of avalue so that current flows through the piezoelectric structure as afunction of an intensity of light from the light source and the amountof strain maintained in the piezoelectric member.
 11. The photodetectorof claim 10, further comprising a non-conductive flexible substrate uponwhich the piezoelectric structure is disposed.
 12. The photodetector ofclaim 11, wherein the flexible substrate comprises polystyrene.
 13. Thephotodetector of claim 10, wherein the piezoelectric structure comprisesa nanowire.
 14. The photodetector of claim 10, wherein the piezoelectricstructure comprises material selected from a group of materialsconsisting of: ZnO, GaN, and a wurtzite structured material.